Multistage carburetors for internal combustion engines



May 16, 1967 A. L. MENNEssoN 3,319,942

MULTISTAGE CARBURETORS FOR INTERNAL COMBUSTION ENGINES Filed April 16, 1955 t /NVFN TOR ra/Q e Apu. /s Mun/:55.41

ATTR/VEY United States Patent() 71, 1 Claim. (Cl. 261-23) The present mvention relates to multistage carburetors for internal combustion engines which comprise, primary and secondary induction pipes in parallel, controlled respectively by primary and secondary throttle valves, each of said throttle valves being disposed downstream of a venturi and of a fuel spray nozzle, the primary throttle valve being actuated by the driver whereas the secondary throttle valve is controlled by mechanical, pneumatic or any other means responsive to the position of the primary throttle valve, in such manner that the secondary throttle valve opens only when the primary throttle valve has been opened, the spray nozzles being fed by a constant level fuel chamber.

It is known that, in such carburetors, for controlling the fuel delivery of each spray nozzle, a fuel metering orifice is placed in each feed conduit connecting the constant level fuel chamber with the corresponding spray nozzle, whereby a primary metering orifice controls the fuel feed suction of the primary spray nozzle and a secondary metering orifice controls the fuel feed suction of the secondary spray nozzle. These two metering systems are independent and consequently the fuel feed suctions are independent.

But, if the cross sectional area of the primary induction pipe is much smaller than that of the secondary induction pipe, the richness of the mixture will increase unduly for small -openings of the secondary throttle valve.

The object of the present invention is to provide a carburetor of the above mentioned type which is capable of correctly adapting the richness of the air and fuel mixture it supplies to the various factors of operation of the engine.

For this purpose, according to the present invention, between the constant level chamber and each of the spray nozzles, there is provided a fuel feed circuit which includes, starting from said chamber, a common portion branching off into as many -conduits as there are spray nozzles, a first metering orifice being provided in this common portion and a second metering orifice in the conduit relative to the primary spray nozzle, whereby the fuel fed to the primary spray nozzle is metered by the first metering orir'ice and then by the second metering orifice, located downstream of the first one.

Preferred embodiments of the present invention will be hereinafter described with reference to the appended drawings, given merely by way of example, and in which:

FIG. 1 is a diagrammatic vertical section of a carburetor made according to the present invention, and

FIG. 2 shows in detailed fashion the means for controlling the throttle valves.

The carburetor comprises, in parallel with each other, a primary conduit 1 and a secondary conduit 2, respectively controlled by a primary throttle valve 3 and a secondary throttle valve 4. These throttle valves are located downstream of venturis 5 and 6. Into these venturis open spray nozzles 7 and 8. The primary throttle valve 3 is actuated by the driver through a rod 9 connected to a lever 10 rigid with the spindle 11 of said primary throttle valve 3. The secondary throttle valve 4 is actuated through means such that it opens only after the primary throttle valve 3 has opened to a given degree.

3,319,942 Patented May 16, 1967 Both of the spray nozzles 7 and 8 are fed with fuel from a constant level fuel chamber 12.

Conduits 1 and 2 have a common air intake 13 protected by an air filter (not Visible on the drawings). Primary conduit 1 has a cross section substantially smaller than that of secondary conduit 2.

The control means interposed between throttle valves 3 and 4 are of the mechanical type and comprise a lever 14 rigid with the primary throttle valve 3 and which, when said valve 3 has reached a position corresponding to a great opening thereof, comes to cooperate, through an abutment 15, with a lever 16 fixed on the spindle 17 of the secondary throttle valve 4. A spring 18 is connected to lever 16 and urges the secondary throttle valve 4 toward its closed position. Thus, as long as the primary throttle valve 3 has not reached a predetermined degree of opening for which abutment 15 comes into contact with lever 16, secondary throttle valve 4 remains closed. On the contrary, when the primary throttle valve 3 has moved beyond said degree of opening, the secondary throttle valve 4 is opened by the cooperation of abutment 15 with lever 16.

Of course, the above described control means have been given merely by way of example and they might be replaced -by equivalent control means, for instance pneumatic control means making use of the suction existing in conduits 1 and 2.

Both of the conduits 1 and 2 are connected in parallel with a common intake 19.

According to the present invention there is provided, between -constant level chamber 12 and each -of the spray nozzles 7 and 8, a fuel feed circuit including, in the portion thereof that starts from chamber 12, a common portion 20 which divides into a primary conduit or well 21 and a secondary conduit 22, and a first metering orifice 23 is inserted in the common conduit 29 whereas a second fuel metering orifice 24 is provided in the conduit or Well 21 corresponding to the primary spray nozzle 7.

Well 21 communicates, at its upper end, with primary spray nozzle 7 and it is provided with an air bleed tube 25 which communicates with the air intake 13 in order t0 emulsify the fuel fed from primary spray nozzle 7.

Conduit 22 leads to a well 26 analogous to well 21. This well 26 communicates, at the upper end thereof, with the secondary spray nozzle 8 and it is provided with an air bleed tube 27 which communicates with the air intake 15 for emulsifying the fuel delivered by the secondary spray nozzle 8.

The carburetor further comprises an idling system which collects fuel from well 21 through a calibrated orifice 28 and air from air intake 13 through a calibrated orice 29, the mixture of this air and of this fuel passing to a conduit 30 which opens into primary conduit 1 through orifices called progression orifices 31 and through an orifice 32 called idling orifice, the last mentioned orifice being adjusted by a screw 33.

This carburetor Works as follows: In known carburetors, metering orifices 23 and 24 are mounted in parallel with respect to the constant level fuel chamber. When the secondary throttle valve 4 starts opening, air passes immediately toward the engine, through secondary conduit 2, without starting the secondary spray system S, because a given suction is required for causing fuel to rise from the constant level in chamber 12, to secondary spray nozzle 8. In order to compensate for the lack of richness that might result from this, it is necessary to adjust the primary spray nozzle 7 so that it supplies a mixture which is a little richer. However, for a slightly greater opening of secondary throttle valve 4, as soon as the secondary spray nozzle 8 begins to deliver fuel, a sudden increase of the richness of the mixture fed into pipe 19 is observed because the secondary spray nozzle 8 starts delivering ice fuel into a mixture which already has a substantially abnormal richness, This phenomenon is the more intensive as, since the cross section of secondary conduit 2 and its venturi 6 is generally greater than that of primary conduit 1 and its venturi S, the metering means correspond ing to well 26 are of a cross section substantially greater than that of the metering means for feeding fuel to well 21. The enrichment observed in some cases is too great for being accepted.

On the contrary, according to the present invention, the metering orifice 24 is placed downstream of metering Orifice 23, whereby, when the secondary spray nozzle S starts working, the fuel it delivers is collected not only through metering orifice 23 from constant level chamber 12 but also partly from well 21 through metering orice 24, or at least the fuel that is supplied by the secondary spray nozzle 8 through metering orifice 23 decreases the amount of fuel that can be collected by spray nozzle 7 through metering orice 24.

Thus it is possible to obtain an air and fuel mixture of practically constant richness.

Of course, the carburetor, instead of being of the downdraft type, might have any othel disposition or inclina tion.

In a general manner while the above description, discloses what are deemed to be practical and efficient embodiments of the present invention, said invention is not limited thereto as there might be `changes made in the arrangement, disposition and form of the parts without departing from the principle `of the invention as comprehended within the scope of the appended claim.

What I claim is:

A multistage carburetor for an internal combustion engine which comprises, in combination,

an air intake,

primary and secondary induction pipes,

primary and secondary throttle valves mounted respectively in said primary and secondary induction pipes, means operative manually for 'actuating said primary throttle valve, means responsive to the position of said primary throttle valve for controlling said secondary throttle valve in such manner that said secondary throttle valve opens when said primary throttle valve has been opened,

primary and secondary venturis mounted respectively in said primary and secondary induction pipes upstream of said throttle valves,

primary and secondary spray nozzles opening respectively into said primary and secondary venturis,

primary and secondary vertical wells connected respectively with said primary and secondary spray nozzles,

primary and secondary vertical air bleed tubes connected with the air intake and dipping respectively in said primary and secondary wells,

a constant level fuel chamber,

a common fuel feed conduit opening from said constant level fuel chamber,

a common fuel metering orifice in said common fuel feed conduit for metering the total fuel How rate through said common fuel feed conduit,

primary and secondary fuel feed conduits starting respectively from the portion of said common fuel feed conduit downstream of said common fuel metering orifice and leading to said primary and secondary vertical Wells, respectively, and

a second fuel metering orifice in said primary fuel feed conduit `below the air bleed tube in said primary well, whereby the fuel flow rate through said primary feed conduit is metered through said common and second fuel metering orifices in series so as to create a small suction upstream of said second metering orice when said secondary throttle valve starts being opened whereby the richness of the mixtures remains approximately constant.

References Cited by the Examiner UNITED STATES PATENTS 2,749,100 6/ 1956 Carlson. 3,081,984 3/1963 Wise.

FOREIGN PATENTS 80,899 5/ 1963 France.

HARRY B. THORNTON, Primary Examiner.

R. R. WEAVER, Assistant Examiner. 

